Island fox description

The island fox is the smallest North American canid, found only on the California Channel Islands. A descendent of the mainland gray fox (Urocyon cinereoargenteus) (2), the island fox evolved into a unique species over 10,000 years ago, retaining similar markings to its ancestor but evolving to be just two-thirds of the size (3). The dorsal coat of the island fox is a grizzled mix of greyish-white and black, while the underside is a dull white. The ears, neck and the sides of the legs are usually cinnamon-coloured, and the chin, borders of the lips and the area between the eyes and nose are black. The tail has a well-defined, black, narrow stripe along the top, greyish sides and is rusty-coloured underneath (4). Males are significantly heavier than females (2), while young foxes normally have a paler and thicker fur coat than adults, and their ears are a darker colour (4). Island foxes moult twice a year, gaining a winter pelage in October to November, which is replaced with a less dense summer pelage during March to May (5).

Related species

Island fox biology

Island foxes are primarily monogamous and mate for life, with a pair sharing a territory until one member of the pair dies. However, while they are socially monogamous, both members of the pair may mate with other adults (7). Most breeding occurs in late February and early March, and 50 to 53 days after mating, the female, or vixen, gives birth to a litter of one to five (usually two to three) kits. Born in the protection of a den, the pups are blind and helpless at birth. The kits emerge from the den at three to four weeks of age and soon begin foraging for food with their parents (4). By late September the kits are independent, and before long, they disperse to their own territory, provided there is a vacant territory and an available mate (7). At around one year of age the young foxes begin to breed. Island foxes have an average life span of four to six years (4).

Island foxes communicate through sight, sound and smell. Vocal communication involves barking and sometimes growling, and signs of dominance or submission are frequently made through facial expressions and body posture. A keen sense of smell plays an important role in the marking of territories, which are scent-marked by urine and faeces, conspicuously positioned on well-traveled paths (4).

This species of fox forages primarily at night, but is also active during the day (2). The island fox feeds on an incredibly wide variety of insects, vertebrates, fruits, and terrestrial molluscs, with the proportions of the diet depending on where the fox lives and the time of year (2)(4).

Species with a similar range

Island fox habitat

The Channel Islands have a Mediterranean-type climate, which is hot and dry in the summer, and cool and wet in the winter (6). The foxes occur in all habitats on the islands, including valley and foothill grasslands, coastal sage scrub, sand dunes, island chaparral, coastal oak and pine forests, and marshes. Dens include ground holes, hollow trees, rock piles, shrubs, caves, and man-made structures (4).

Island fox threats

Numbers of island foxes declined at alarming rates since 1994, with four of the six subspecies declining by as much as 95 percent. The primary threats causing these devastating declines were predation by golden eagles (Aquila chrysaetos) on the northern Channel Islands, canine distemper virus (CDV) on Santa Catalina Island, and collision with vehicles on San Clemente and San Nicolas Islands (2)(8).

Golden eagles had not always lived on the Channel Islands, but were attracted there by the introduction of wild pigs (Sus scrofa) (9). These impressive birds of prey colonized the northern Channel Islands in 1994 and began to prey heavily on foxes, quickly bringing the island fox to the brink of extinction (10). By 1999, only 14 individuals of the San Miguel subspecies remained (11).

On Santa Catalina Island, the introduction of CDV, (believed to be brought to the island by a domestic dog), caused the deaths of about 90 percent of the fox population in just one year, (1999 to 2000) (12). The introduction and spread of CDV, and other canine diseases, remains a potential threat to all the island fox subspecies (8).

In 1999, 32 foxes on San Clemente Island were either culled or permanently removed from the island to zoological institutions, as part of a programme to protect the endangered bird, the loggerhead shrike (Lanius ludovicianus). Another 49 were temporarily held in small pens while the shrikes were nesting, and in 2000, a further 71 foxes were held again. This practice has since been stopped, but the disruption this caused to reproduction and social systems is believed to have significantly affected the San Clemente Island fox population and contributed to its current Critically Endangered status (13).

Like any small, isolated island populations, the island fox remains extremely vulnerable to any catastrophic mortality source, be it predation, canine disease, or environmental extremes (1).

Island fox conservation

The island fox is listed by the state of California as a threatened species (1), and the islands themselves also receive protection. Santa Rosa, San Miguel and Santa Cruz are part of the Channel Islands National Park, which is protected by the U.S National Park Service, and the western portion of Santa Cruz Island is also protected by The Nature Conservancy. Dogs and cats are prohibited from being brought into the Channel Islands National Park, in order to prevent infections from being transmitted to the foxes (6). Santa Catalina Island is owned and managed by the Catalina Island Conservancy (14), and the remaining two islands, San Nicolas and San Clemente, are owned and managed by the U.S. Navy (1).

Captive breeding and reintroduction programmes on San Miguel, Santa Rosa and Santa Cruz Islands, along with programmes to remove and relocate golden eagles and reintroduce bald eagles, have been a remarkable success. The San Miguel population, which was once the most endangered, made such a strong recovery through the captive breeding programme, and the wild population was doing so well, that all releasable individuals were returned to the wild in July 2007. On Santa Cruz, many captive bred foxes have also been returned to the wild. Unfortunately, a number of these have been the victims of continued golden eagle predation, but with January 2007 seeing the removal of all the feral pigs, it is hoped that there will be less motivation for any golden eagles to remain on the island (11).

On Santa Catalina, less than one year after the CDV-caused decline in the fox population, the Institute for Wildlife Studies began an island-wide vaccination programme against this disease. In addition, a captive breeding programme was initiated to aid in repopulating the island. The programme has been a resounding success (12), and the population continues to recover from its near-catastrophic decline (11). With the continuation of such determined conservation efforts, hopefully the island fox will one day serve as an example of how critically endangered species can be pulled back from the brink of extinction.

Authentication

Glossary

Canid

Amember of the Canidae family (the ‘dog’ family); which includes all living dogs, wolves, jackals and foxes.

Molluscs

A diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.

Monogamous

Mating with a single partner.

Natal

Site of birth.

Subspecies

A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

Roemer, G.W. and Donlan, C.J. (2004) Biology, policy and law in endangered species conservation. I. The case of the island fox on the northern Channel Islands. Endangered Species Update, 21(1): 23 - 31.

Roemer, G.W. and Donlan, C.J. (2005) Biology, policy and law in endangered species conservation: II. A case history in adaptive management of the island fox on Santa Catalina Island, California. Endangered Species Update, 22(4): 144 - 156.

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